The state of the art of the various methods for joining SiC parts has been described in patent application US2010/0055498. Typically these methods require that a joining compound to be applied between the SiC parts and fired in a reducing atmosphere (e.g., nitrogen, argon, vacuum) due to the reactivity of the compounds with the oxygen in air. The method described in US2010/0055498 consists of preparing a glass fit (with composition SiO2/Al2O3/CaO or Al2O3/CaO/MgO), mixing the fit with an organic binder, applying the frit/binder to the SiC parts to be joined and firing in air at a temperature between 1100 and 1650° C. The resulting joint is described as being leak-tight at temperatures up to 1200° C. depending on the composition of the fit.
The maximum operating temperature of 1200° C. in the frit sealing method described above is a limiting factor for some applications such as the consolidation of optical fiber preforms which can require temperatures above 1450° C. for several hours. The size of the SiC vessel for the fiber preform for such an application would be 12 to 18 inches in diameter and 12 to 18 feet in length. Such a large SiC part cannot be made with the current manufacturing process, so it must be made by assembling multiple tube sections. Thus, it is desirable to use a joint material that enables the formation of SiC vessels having a diameter of 12-18 inches and a length of 12-18 feet from shorter lengths of SiC tubing. The joint material should be usable at temperatures of up to at least 1500° C. and provide leak-tight seals.